The application range of magnetic recording drives, such as magnetic disk drives, flexible disk drives and magnetic tape drives, has recently been significantly extended, making these magnetic recording drives more important. For magnetic recording media used in these drives, efforts have been made to markedly improve recording density. In particular, since the introduction of an MR head and a PRML technique, surface recording density has been further significantly increased. In recent years, a GMR head and a TMR head have also been introduced to increase the recording density at a rate of as much as 100% per year. The magnetic recording media have been demanded to achieve a much higher recording density in the future. Thus, there has been a demand for an increase in the coersive force, signal-to-noise ratio (SNR) and resolution of a magnetic recording layer. Furthermore, efforts have been made to increase linear recording density as well as track density in order to improve the surface recording density.
The latest magnetic recording drives have a track density of as much as 110 kTPI. However, increasing the track density is disadvantageously likely to cause magnetically recorded data in adjacent tracks to interfere with each other. A magnetization transition region in the boundary between the adjacent tracks may then serves as a noise source to reduce the SNR. This leads directly to a decrease in bit error rate, hindering the enhancement of the recording density.
To increase the surface recording density, it is necessary to reduce the size of recording bits on the magnetic recording medium to ensure as high saturation magnetization and as large a magnetic film thickness as possible for each recording bit. However, a reduction in the size of recording bits may disadvantageously decrease the minimum magnetization volume per bit, resulting in heat fluctuation. Magnetization reversal may men occur to eliminate the recorded data.
Furthermore, the resulting decrease in inter-track distance leads to the need for a very highly accurate track servo technique for the magnetic recording drive. Further, a method is generally used, which uses a wide recording range and a reproducing range that is narrower than the recording range in order to eliminate the adverse effect by the adjacent tracks as much as possible. This method can suppress the effect between tracks to the minimum. However, this may disadvantageously make it difficult to obtain sufficient reproduction outputs and to thus ensure a sufficient SNR.
To avoid the heat fluctuation problem and to ensure a sufficient SNR and sufficient outputs, an attempt has been made to form recesses and protrusions on the surface of the recording medium along the tracks to physically separate the recording tracks from one another in order to increase the track density. This technique is hereinafter referred to as a discrete track method. A magnetic recording medium manufactured by the discrete track method is hereinafter referred to as a discrete track medium.
A known example of the discrete track medium is a magnetic recording medium formed on a nonmagnetic substrate having recess and protrusion patterns on a surface thereof to form physically separate magnetic recording tracks and servo signal patterns (see, for example, JP-A 2004-164692).
This magnetic recording medium has a ferromagnetic layer formed, via a soft magnetic layer, on the surface of a substrate on which a plurality of recesses and protrusions are formed. A protective film is formed on the surface of the substrate. The magnetic recording medium has a magnetic recording region formed thereon in the area of the protrusions and physically separated from surroundings.
The magnetic recording medium can inhibit the formation of magnetic domain walls in the soft magnetic layer, avoiding the adverse effect by heat fluctuation and the interference between the adjacent signals. This makes it possible to provide a high-density magnetic recording medium mat can minimize possible noise.
The discrete track method includes a method of forming tracks after forming a magnetic recording medium made up of a number of layers of thin films and a method of forming thin films for the magnetic recording medium after forming recess and protrusion patterns directly on the substrate surface or in a mm film layer mw JP-A 2004-178793 and JP-A 2004-178794). The former method is often called a magnetic layer processing method and performs physical processing on the surface after the formation of the medium. Unfortunately, the medium is thus prone to be contaminated during the manufacturing process, which is very complicated. The latter method is often called an embossing method. This method prevents the medium from being contaminated during the manufacturing process. However, the film formed takes over the recess and protrusion shapes formed on the substrate, preventing the stabilization of the floating posture and height of a recording and reproducing head performing the recording and reproducing operations while floating over the medium.
A method has also been disclosed, which involves forming inter-track regions in the discrete track medium by implanting nitrogen or oxygen ions in the preformed magnetic layer or irradiating the magnetic layer with a laser (see JP-A HEI 5-205257). However, the inter-track regions formed by this method offer reduced saturation magnetization but increased coersive force. Consequently, an insufficient magnetization state remains, resulting in blurring when information is written on the magnetic track portion.
A method has also been disclosed, which involves manufacturing what is called a patterned medium having magnetic recording patterns arranged with a specified bit-by-bit regularity wherein the magnetic recording pattern are formed by etching based on ion irradiation (see IEICE Technical Report MR2005-55 (2006-02), pp. 21-26 (The Institute of Electronics, Information and Communication Engineers)). However, even with this method, disadvantageously, the magnetic recording medium may be contaminated during the manufacturing process. Furthermore, the smoothness of the surface may be degraded.
For magnetic recording apparatuses that face technical difficulties associated with the increased recording density, the present invention drastically increases the recording density while ensuring recording and reproducing properties equivalent or superior to those achieved by the conventional techniques. The present invention also reduces the coersive force and remanent magnetization in the inter-pattern regions to the minimum to prevent possible blurring during magnetic recording. This increases the surface recording density. In particular, for discrete-track magnetic recording media manufactured by forming recesses and protrusions on a magnetic layer preformed on the substrate, the present invention eliminates a magnetic layer removing step executed for the conventional magnetic layer processing method, substantially simplifying the manufacturing process. The present invention also provides a manufacturing method with reduced contamination risks and a useful magnetic recording medium with an excellent head floating property.
Through dedicated efforts to accomplish the above object, the present inventors have reached the present invention.